1. Field of the Invention
The present invention relates to an integrated circuit for processing signals in a video camera and, more specifically, to an integrated signal processing circuit for processing in a digital manner various signals in a video camera having an electronic zooming function.
2. Description of the Background Art
A conventional digital video camera includes two integrated circuits, that is, an integrated circuit for processing luminance signals and an integrated circuit for processing color signals, for processing various signals therein. The integrated circuit for processing luminance signals requires two 1H (H represents horizontal period of a video signal) delay elements for effecting digital signal processing such as contour enhancement in vertical direction of the image. The integrated circuit for processing color signals also requires two 1H delay elements for effecting digital signal processing such as simultaneous processing of color signals.
Since such a 1H delay element is generally formed of a random access memory (RAM), it occupies a large area in the integrated circuit. Therefore, a technique allowing sharing of two 1H delay elements for luminance signal processing and color signal processing has been proposed, for example, in National Technical Report volume 36, No. 3, pp 85 to 90, June 1990.
In recent video cameras (especially in VTRs containing cameras, also called camcoders), an electronic zooming function is employed in addition to the conventional optical zooming function in order to improve magnification rate of zooming as a whole, while keeping the magnification rate of the optical zoom lens itself constant. The electronic zooming function includes interpolation of video information of a selected area of the picked up image in the vertical and horizontal directions to provide an enlarged image. It is also used for a so called hand shake correcting control in which fluctuation of peripheral portions of the picked up image caused by hand shake is eliminated to record stable image at the central area.
In order to realize such an electronic zooming function, a field memory for temporarily storing image signal outputs from an image sensing device is provided in a preceding stage of the above mentioned luminance signal and color signal processing circuits, and an integrated circuit for effecting interpolation for synthesizing image information of new display points which become necessary to effect electronic zooming is provided in the succeeding stage of the luminance signal and color signal processing circuits. The integrated circuit for interpolation further requires two more 1H delay elements to effect interpolation.
Namely, in the digital video cameral such as disclosed in the above mentioned document, a total of three integrated circuits are necessary for luminance signal processing, color signal processing and interpolation so as to realize the electronic zooming function, which prevents a reduction in size of the camera itself.
Therefore, it is necessary to incorporate various functions of these three integrated circuits into one integrated circuit so as to reduce the size of the signal processing system in the video camera. However, since two 1H delay elements (RAMs) are necessary for processing luminance signals and color signals and two more 1H delay elements are necessary for interpolation, four 1H delay elements (RAMs) must be provided in one integrated circuit in order to process all of the above mentioned signals in one integrated circuit. The 1H delay element (RAM) itself occupies a very large area on a chip as shown in the chip layout of FIG. 5(a) in page 89 of the aforementioned document, and therefore, provision of four 1H delay elements (RAMs) for processing various signals makes difficult one-chip implementation of the signal processing system of a digital video camera.